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The load-multiple instruction that essentially performs the switch_to operation in ARM mode, by loading all callee save registers as well the stack pointer and the program counter, is split into 3 separate loads for Thumb-2, with the IP register used as a temporary to capture the value of R4 before it gets overwritten. We can clean this up a bit, by sticking with a single LDMIA instruction, but one that pops SP and PC into IP and LR, respectively, and by using ordinary move register and branch instructions to get those values into SP and PC. This also allows us to move the set_current call closer to the assignment of SP, reducing the window where those are mutually out of sync. This is especially relevant for CONFIG_VMAP_STACK, which is being introduced in a subsequent patch, where we need to issue a load that might fault from the new stack while running from the old one, to ensure that stale PMD entries in the VMALLOC space are synced up. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Tested-by: Keith Packard <keithpac@amazon.com> Tested-by: Marc Zyngier <maz@kernel.org> Tested-by: Vladimir Murzin <vladimir.murzin@arm.com> # ARMv7M
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.